Electronic devices fabricated from semiconducting diamond offer significant potential for high power and high frequency device applications. This is because diamond possesses a preferred combination of properties such as wide bandgap (5.5 eV), high electron and hole mobility (2000 cm.sup.2 V.sup.-1 sec.sup.-1), high electron saturation velocity (2.times.10.sup.7 cm sec.sup.-1) and high breakdown voltage (10.sup.7 V cm.sup.-1), as compared to other conventional semiconductors such as silicon, germanium and gallium arsenide.
Examples of electronic devices formed in diamond include U.S. Pat. No. 5,072,264 to Jones entitled "Diamond Transistor and Method of Manufacture Thereof", which discloses diamond MISFETs and MESFETs. In particular, the Jones patent discloses a diamond MISFET having a wide bandgap insulating region on a p-type diamond substrate and a metallic layer on the insulating region. U.S. Pat. No. 5,114,871 to Jones entitled "Manufacturing Diamond Electronic Devices" also discloses a method of manufacturing a diamond MISFET having a p-type diamond substrate and an insulating layer and metal layer thereon. U.S. Pat. No. 5,107,315 to Kumagai et al. entitled "MIS Type Diamond Field-Effect-Transistor With A Diamond Insulator Undercoat" further discloses a diamond MISFET on a diamond insulator undercoat. Polycrystalline diamond MOSFETs are also disclosed in an article by A. J. Tessmer, K. Das and coinventor D. L. Dreifus entitled Polycrystalline diamond field-effect transistors, Diamond and Related Materials, (1992), pp. 89-92.
Unfortunately, devices having MIS gate structures formed on semiconducting diamond typically suffer from parasitic effects such as high leakage currents across or parallel to the semiconducting diamond/MIS gate structure interface. These parasitic effects can also inhibit complete turn-off and accumulation mode operation of FETs, as described in articles by G. Sh. Gildenblat and S. A. Grot et al. entitled: "High Temperature Thin-Film Diamond Field-Effect Transistor Fabricated Using a Selective Growth Method", IEEE Electron Device Letters, Vol. 12, No. 2, (1991), pp. 37-39; and "Diamond Thin-Film Recessed Gate Field-Effect Transistors Fabricated by Electron Cyclotron Resonance Plasma Etching", IEEE Electron Device Letters, Vol. 13, No. 9, (1992), pp. 462-464. These articles also disclose that parasitic conduction is a common feature in such conventional diamond FETs, but the physical cause is unknown and under investigation.
Thus, notwithstanding the above described attempts to fabricate diamond semiconductor devices having MIS gate structures, there continues to be need for diamond semiconductor devices which have MIS gate structures thereon, but also have substantially reduced parasitic effects.